Heavy Quarks Above the Top at the Tevatron

TL;DR

This work investigates heavy vector-like quarks that mix with light SM quarks in warped extra-dimensional models, focusing on single production at the Tevatron via electroweak processes enhanced by valence-quark PDFs. A model-independent framework is developed with two vector-like doublets and couplings $\,\kappa_{qQ}=(v/m_Q)\tilde{\kappa}_{qQ}$, yielding measurable cross sections for $m_Q$ up to several hundred GeV; the authors show that 4–8 fb$^{-1}$ can achieve 5$\sigma$ discovery for $m_Q$ in the range 580–630 GeV (for $S_Q^{CC}=1$) and up to 710 GeV (for $S_Q^{CC}=2$). They define the observable signal via $\sigma(pp\to q_1 q_2 f\bar f)=S^{CC}_{Q}\,\sigma^{CC}_{prodn}\,Br(V\to f\bar f)$ and analyze decay channels $D\to W u$, $Z d$, $h d$ and $U\to W d$, $Z u$, $h u$, with emphasis on gauge-boson final states and mass-reconstruction techniques. The study demonstrates that single-production channels can rival or exceed pair production in this mass regime, and provides strategies for charge identification and background suppression, offering practical guidance for Tevatron searches and for similar analyses at the LHC.

Abstract

Recent developments in models with warped extra dimensions have opened new possibilities for vector-like quark studies at hadron colliders. These new vector-like quarks can mix sizably with light Standard Model quarks without violating low energy constraints. We perform a model-independent analysis to determine the Tevatron reach in the search for new quarks. We find that the Tevatron has great potential to observe such quarks via their electroweak single production due to their mixing with valence quarks. With 4 (8) fb-1 integrated luminosity, one may reach a 5σstatistical significance for a heavy quark of mass 580 (630) GeV if the heavy quark-Standard Model quark mixing parameter is order one.

Figures (4)

• Figure 1: Total cross sections for heavy quark production versus its mass $m_Q^{}$ at the Tevatron with $\sqrt s=1.96$ TeV in $p\bar{p}$ collisions. Solid curves are for single production via charged current (CC) of $D+\overline D$ (upper) and $U+\overline U$ (lower); dashed curves are for single production via neutral current (NC) of $U+\overline U$ (upper) and $D+\overline D$ (lower); and the dotted curve is for pair production from QCD.
• Figure 2: (a) Top left: pseudo-rapidity distribution for the soft jet. (b) top right: azimuthal angle between $p_T(\ell)$ and $p\!\!\!\slash_{T}$ (c) bottom left: invariant mass distribution for the reconstructed heavy quark from visible $Z$ decay (d) bottom right: transverse mass distributions for the reconstructed heavy quark.
• Figure 3: Sensitivity plots in the plane of model-dependent parameter $S^{ CC}_{ Q}$ and heavy quark mass $m_Q$ for CC decay mode of heavy quark with 4 fb$^{-1}$ and 8 fb$^{-1}$ integrated luminosity. The top set (red) is for $m_U$ versus $S^{ CC}_{ U}$ and bottom set (black) is for $m_D$ versus $S^{ CC}_{ D}$.
• Figure 4: Sensitivity plots in the plane of model-dependent parameter $S^{ NC}_{ Q}$ and heavy quark mass $m_Q$ for NC decay mode of heavy quark with 4 fb$^{-1}$ and 8 fb$^{-1}$ integrated luminosity. The top set (black) is for $m_D$ versus $S^{ NC}_{ D}$ and bottom set (red) is for $m_U$ versus $S^{ NC}_{ U}$.